Abstract
Iron mixed-valence complex ( n-C 3H 7) 4N-[Fe IIFe III(dto) 3] (dto = C 2O 2S 2) shows a new-type of phase transition coupled with spin and charge around 120 K, where the charge transfer between the Fe II and F III sites occurs reversibly, and shows the ferromagnetic transition at 7 K. The charge transfer phase transition at 120 K can be explained by the crossover of free energy between the higher temperature phase with Fe II ( S = 2) and Fe III ( S = 1/2) and the lower temperature phase with Fe II ( S = 0) and Fe III ( S = 5/2). Recently, we have succeeded in preparing an ( n-C 3H 7) 4N[Fe IIFe III(dto) 3] analogue, ( n-C 3H 7) 4N[Fe IIFe III(tto) 3] (tto = C 2OS 3). From the magnetic susceptibility measurement, ( n-C 3H 7) 4N[Fe IIFe III(tto) 3] shows the ferromagnetic phase transition at 9.5 K, There is a hysteresis behavior in the wide range of temperature, whose upper limit cannot be observed obviously below 340 K. This result suggests that the bistability between the higher and the lower temperature phases in dit complex is realized for tto complex at room temperature region. Judging from ESR and 57Fe Mössbauer spectra on heating process, the spin states are consistent with the lower temperature phase with Fe II ( S = 0) and Fe III ( S = 5/2) between 2 K and 340 K.
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